I’m not familiar with Home Assistant as I’m really focused on the SmartThings platform so I’m afraid that I don’t have a plug and play solution for you.
All I can say is that my zoning smartapps can expose rooms as virtual zone devices (1 to many rooms) with the thermostatSetpoint capability. I don’t know if it’s sufficient for your needs or not.
In the zoning smartapps, there are many safeguards in place to avoid closing too many vents at the same time.
But again, all the smartapps were designed for the SmartThings ecosystem, not to be used by a bridge to Home Assistant.
For more information about My zoning smartapps, refer to the following thread:
I’d recommend looking into ScheduleRoomTempControl or ecobeeSetZoneWithSchedule depending on your needs.
P. S. You couldn’t create the thermostat because you contributed to the Flair vent bundle which doesn’t include the Flair tstat DTH. Anyway, for your use case, this wouldn’t help.